The present invention relates to devices which cause linear motion of a machine component in general, and to devices employing a ratchet mechanism in particular.
Papermaking is usually performed on a papermaking machine which manufactures a paper web many meters wide, typically 5-10 meters wide in a cross machine direction which is perpendicular to the direction defined by the motion of the paper web as it is being formed. Within the papermaking machine, for most processes, every effort is made to treat the entire width of the paper web uniformly to insure cross machine direction uniformity in the paper web being formed. However for some processes within the papermaking machine it is not necessary or cost-effective to perform a particular operation simultaneously on the entire cross machine direction width of the web. For example, when properties of the web are monitored in the cross machine direction it is often sufficient to have the monitoring instrument be moved from one edge of the paper web to the other, traversing back and forth across the web in a systematic manner. In addition, instruments which measure web caliper, web density, web moisture, web curl, etc. can be periodically scanned in the cross machine direction over the paper web. Cleaning operations which need not be continuous but which are necessary to maintain the functionality of a roll, an air knife, a fabric, a felt or a wire, can be performed with a cleaning unit which is moved back and forth in the cross machine direction.
Because of the wide width of the papermaking machine, of up to around 10 m, the test instrument or cleaning unit will typically be positioned on machine ways, linear bearings, or wheels mounted to a cross machine direction bridge which provides the required stiffness and resistance to vibration necessary for accurate positioning of a scanning instrument or cleaning device. The remaining necessity is some means of driving the test instrument or cleaning unit back and forth in a cross machine direction. Known approaches are the use of a machine screw, a rack and pinon gear arrangement, or a belt or cable drive, however these approaches require expensive components, or suffer from a lack of reliability, require significant maintenance or utilize an excessive amount of space. What is needed is a mechanically simple, low-cost, compact, and reliable means for traversing a piece of equipment back and forth in the cross machine direction over the entire width of a paper web in a papermaking machine.